The present invention relates to a device for cooling the salient-type rotor poles of an electrical machine such as synchronous machine.
The conventional path of the air circulation is the following: The radial air ducts in the stator core, the air/water heat exchangers, the return channels over and below the stator leading to the the room above and below the rotor, axially through inlet openings into the spider, radially through the rotor rim ducts, radially through the interpolar space between the salient poles, into the airgap between rotor and stator, and finally back into the radial air ducts in the stator core.
Additional flow paths may start from the spider, radially along the axial end surface of rotor rim, axially into the interpolar space and airgap between the rotor and stator. An alternative route may start from the the return channels above and below the stator, through fans mounted on the axial ends of the rim, into the interpolar space and airgap.
The ventilation system mentioned above has to take care of, among others, the cooling of the salient poles. The flow between the poles is complicated, because of the complex geometry and the fact that the poles are acting as pressure producing radial fan blades, increasing the circumferrential velocity component of the air. Therefore, the flow of air in the interpolar space is not only an axial or radial movement but it has also a rotational component perpendicular to the rotor shaft.
In order to organize the complex movement of air in the interpolar space it was proposed to use interpolar baffles extending over the whole axial length of the interpolar space. (Not patented). The cross-section of the known baffles, is a "U" - form. The "U" is closed against the rotor rim, and open against the internal surface of stator. The heads of the screws anchoring the baffle to the rim are located inside of the "U". The idea behind this solution is to guide the air, coming from the radial rim ducts, along the surface of the salient poles, providing an even and effective heat transfer from the pole surface to the cooling air. This objective is usually achieved, but the generated energy losses in turbulance at the open end of "U" section are considerable.